The use of drill jigs or drilling templates to aid in the installation of door operating hardware is well known. Door operating hardware, e.g., door knobs and locks, is usually mounted on a door using through bolts. The through bolts engage mounting plates on either side of a door. Through holes must be provided in the door for these through bolts, as well as for other parts of the door operating hardware.
Proper installation of the door operating hardware requires accurate formation of these mounting holes. The mounting holes not only must be formed in the right place, but also must be formed perpendicular or "square" to the side of the door.
Additionally, the mounting holes must be drilled entirely through a door so that the screws or bolts placed in these holes can interconnect the hardware parts that go on the exterior side of the door with those that go on the interior side of the door.
The relative thickness of a door, the tendency of a drill to walk, and error in human judgement, however, make the accurate formation of these holes a very difficult task. Unfortunately, failure to drill accurate holes can have severe consequences. For example, if the hole centers are not properly positioned, installation of, e.g., a handle or dead bolt lock, becomes very difficult and often requires enlarging the hole diameter, thereby resulting in a sloppy fit. If the installation handles are not drilled through the door exactly square, the interior and exterior parts of the door hardware will not be properly interconnected. Even if the holes are only slightly off-square, they usually have to be redrilled oversize or reamed out to enable the handle or lock to be installed and operate freely. However, if the holes are badly off square, a fix may be impossible without ruining the appearance of the door.
Because of the difficulty of drilling accurate mounting holes, a drilling aid in the form of a drill jig or drilling template is usually provided with purchased door hardware. These drilling aids usually comprise a paper or light cardboard template, The templates are taped to the door or held in place manually in the location where a handle or lock is to be installed. Using a pointed instrument, such as an awl or center punch, the centers of the required holes to be drilled, can be marked on the door.
Plastic jigs or templates are also known. Such plastic jigs may include drill bushings for guiding a drill bit through a door and providing a specified distance between mounting holes. Such drill jigs are typically clamped to the door with an external clamp in the location where the door hardware, e.g., a dead bolt, is to be installed. A drill bit is inserted through the drill bushings to form the required mounting holes.
The prior art drill jigs and drilling templates suffer from a number of disadvantages. In particular, using a paper template, it is easy to mismark the hole locations. Paper templates also only provide marking points for the mounting holes. Paper templates still allow improper alignment, perpendicularity or sizing of the mounting holes. Additionally, paper templates provide no protection from damage to a door that might occur during a drilling operation. Paper templates are difficult to position properly on the door. They also easily tear and crease making them difficult to use. The fragility of paper templates also makes them unsuitable for repeated use. This inability to reuse a template is particularly irksome in the construction of an office or apartment building, where many sets of door hardware have to be installed. It can also be troublesome for the homeowner whose first attempt at marking the mounting holes has been unsuccessful and who therefore needs to reuse the template.
Plastic templates or jigs provide some advantages over paper templates. In particular, they are more durable and aid in the proper sizing and positioning of mounting holes. However, plastic templates also suffer from a large number of disadvantages. For example, by the time a plastic template is used for a second or third time, it tends to become warm and flexible during the drilling operation. This leads to inaccuracies in the size and positioning of the mounting holes. The high stresses created during a drilling operation also usually mean that plastic jigs tend to break after only four or five uses. Additionally, even though a plastic jig may be reusable, it can typically be used only with one particular type of door hardware and one type of door. This can be inconvenient during construction where many types of door hardware and doors may have to be installed. It can also be inconvenient for carpenters or contractors or the like who install many types of door hardware and doors in the course of their employment. Like paper templates, plastic jigs, too, are difficult to position properly and require the use of external mounting devices such as C-clamps. Likewise they provide no protection from damage incurred during a drilling operation. The holes formed using a plastic jig are also susceptible to inaccuracy because of the manner in which plastic drill jigs require a hole to be drilled. Specifically, a plastic jig is first put on one side of the door and a hole is drilled through half of the door thickness. The plastic jig is then placed on the opposite side of the door, hopefully so that the bushing on the plastic jig is aligned with the previously drilled hole, and the door is again drilled halfway through in order to form a through hole. Thus, the installation procedure using a plastic jig is awkward and inefficient. Moreover, with plastic jigs substantial opportunity exists that the plastic jig will be misaligned and that proper through holes will not be formed.